Hydraulically expansible hollow rivet



1949 J. A. VARNEY ETAL 2,492,605

HYDRAULICALLY EXFANSIBLE HOLLOW RIVET Filed Nov. 10, 1941 l/vve/vroms /GO dus T/N ARA/0L0 l/ARNAIY F250 M I/ARNL'Y or NORMANJ HOLTER A TT'O RN: K5.

Patented Dec. 27, 1949 2,492,605 HYDRAULICALLY EXPANSIBLE HOLLOVI" Justin Arnold Varncy and Fred M. Varney,

Angeles, and Norman J., Holter, Beverly Hills,

Calif assignors to United Air Lines, cago, IlL, acorporatlon of Delaware Application November 10, ialrscrlsl No, 41am 9 mm. (cl. 8

The present inventionrelates to rivets, especially self-heading rivets, and is particularly dif rected to such a rivet adapted tobe set by hydraulicaction.

In the procedure of settlngra-conventional rivet having a preformed'hea'd; a structurally eflicient second head is-form'ed on the leadin end of the rivet by the application of a suitable impact tool and theaxial compression of the rivet between the impact tooland the usualbucking bar causes the shank ofthe rivet to expand into snug fit with the surrounding work material In so-called blind riveting a rivet is applied to the. work from one side with no opportunity. to apply a bucking bar to the rivet from the opposite side of the work and the riv'et-mustlbe designed for a heading operation'executed from theside of application.

Inc.', v

More specific objects of our'cinve'ntion are to solve certain difllcult problems in designing a rivet for hydraulic operation; These problems include. the following: to'trap in therivet a suitable fluent material substantlally free of air or-oth v p Y compressible ingredient: to'trap inlthe rivet, the I iprecise volume of the lluentmaterialrequired for agiven predetermined hydraulic eflect; to pro-'- clude escape of the measured volume of fluent material, aproblern that i especially important" because the measured volume is usually exceedn ly small-and is especially 'diflcult since he,-

mendous pressurelis generated the setting opl eration; toprovide arlvet thatis of hollow con-' 1 struction for hydraulic operationfand yet to achieve a finished rivet as strongas; or stronger Various mechanical arrangements have been employed to permit rivets to be headed from the side of application. Mechanicaily'operatedrivets of this type are usually weaker than conventional rivets, do not provide structurally efllcient secthan, a' conventional rivet; and to provide a-selfheading hydraulic rivet that willnot only expand to form a second inner headbut-will also expand along its shank into satisfactory pressuralcon.-

1 tact with the surrounding work material.

Our rivet, which is adapted for insertion v through registered bores or rivet holes of a pluond heads, do not expand at their shanksinto tight fit with the surrounding work material,

and generally require both special tools and advanced skill.

-.said body'having a blind bore extending longi- One line of development has led to explosive rivets. An explosive rivet of the prevalent type has the disadvantage of requiring heat applica-' tion by a special tool, which must be heated to an operative temperature at the beginning of'a work period, and the explosion of the rivet neither 1 produces a structurally eillcient' second head nor results in satisfactory expansion of the rivet shank against the surrounding work material.

Since the shank of an explosive rivet does-notexpand, dimensions 'of rlvet'holes must be closely controlled and two holes must ;be separately j drilled in preparation'for each rivet. An /explosive rivet, furthermore, is necessarily designed for a given total thicknessof. the two members to be riveted with verylittle latitudepermitted.

The usual tolera'ncein gripleng th is only .005

over and .0'l5un'der. Finally, great-care'must be exercised to have all in pressural contact at the moment the rivet explodes.

The general object ofou'r' invention is to provide a'n inexpensiveself-he'ading rivet in which the physical properties of conventional bucked rivets areapproximated if not exceeded, We propose to provide a dependable and exceptionally rality of members for interconnecting the members, may be broadlygdescribed as comprising a rivet body with a shank and preformed head.

tudinally through the head into the shank, a

mass of fluent material inthebllnd bore, and a pin or plunger'ad'apted to be driven-into the blind bore against theifluent material to displace j the fluent material outwardly,- thereby --to radially expand the shank of therivet in theend zone beyond said registeredrivet holes into greater diameter than the registered holes.

, with reference to a rivet constructed in accord with this descriptionthe specific objectsof our invention include the following: toprovide a pin,-

and-rivet combination in which the pin cooper: ates with the rivet to cause any excess quantity of the fluent materialto be extruded automati cally when the pinls inserted; tojprovide such a' pln-and-rlvet combination in'which the pin functions as a valve member-to cut olfextrus'ion at precisely the point. at which the fluent material is reduced to a desired predetermined volume; to

' provide such .arcombination in which fitting of thevguent materialfunder exceedingly high pres-f suresis assured without the ne :esslty.of mainstrong self-heading rivet that may be rapidly set v by an unskilled workman without using heat and without using any special setting tool.

the pin in the rivet effective against leakage of taming close fits'between members ofthe rivet;

to provide such a combin'ationin which the pin has the dual function of a hydraulic-plunger to displace the fluent material, and a mechanical wedge to expand the rivet shank; to provide such.-

a combination in which it is necessary merely to insert the pin and drive the pin flush with the preformed head of the rivet to insure elimination of air, extrusion of excess fluent material, effective trapping of the desired residual quantity of the fluent material; to provide such a combination in which it is necessary merely to drive the pin home; to insure the precise extent of displacement of the trapped fluent material required to expand the inner end of the rivet into an effective second head; and to provide such a combination in which the pin is permanently seated in the rivet in a manner to hydraulically lock the inner or second head of the rivet against contraction from its expanded state.

In one practice of our invention, the material for hydraulic action is trap d in the rivet by the rivet pin before the rivet is placed in stock, and the assembled rivet is heated to make the trapped material fluent at the time of installation. One object'of our invention in this par- 'ticular practice is to provide for entrapment of the material and yet to permit the material to (Expand under heat without pushing the rivet pin outward.

'lf'he various objects and advantages of our invention including those mentioned above will be apparent in the detailed description to follow, taken with the accompanying drawing.

'In' the drawing,wliich is-to be regarded as merelyj'illustrativez' f Fig.1 is alongitudinal section of a rivet body employed in the preferred practice of our invention;,' Fig. 2 is a similar view showing the rivet body provided with a tapered pin and inserted through registered bores in two sheets of work material; I

Fig. 3 is a similar-'view showing the pin advanced into the rivet to a point to trap the fluent material therein;

Fig. 4 is a similar view showing the pin driven completely into the rivet for the purpose of setting the rivet;

Fig. 5 is a view similar to Fig. 2 showing a modi fled form of our rivet combination;

Fig. 6 is a similar view showing a second modiflcation of our rivet combination; and

Fig. '1 is a similar view of a third modification V of our rivet combination.

The preferred practice of our invention exemplified by Figs. 1-4 is characterized by the concept of employing a'tapered pin in the above-mentioned combination, which-employment accomplishes further objects and achieves further advantages of first importance.

In providing for automatic release of excess fluent material, it becomes necessary to design the pin to serve as a valve member to cut off and mined residual quantity of the fluent material.

form of our invention is to avoid a simple slidevalve action in favor of a more efficient mode of operation. A tapered pin in combination with a bore hole having an entrance of complementary taper permits a. valve action that is distinctly difierent from simple slide-valve action and is especially advantageous in a hydraulic rivet. During the initial stage of insertion of the tapered pin into the tapered rivet bore, an annular passage is formed by the rivet and bore to permit the fluent material to flow freely to the entrance of the bore, but at a predetermined point in the inward progress of the pin two conical sealing surfaces of substantial axial extent come into instantaneous mutual contact and instantly a wedging action occurs to place the axially extensive sealing surfaces under uniform radial pressure of such magnitude as to preclude any further extrusion of the fluent material.

Preferably a pin that is oversize with respect to the rivet bore is employed in the various practices of our invention. Tapering the oversize pin and/or tapering the entrance to the rivet bore into which the pin is inserted provides for efiectively maintaining radial sealing pressure continuously as the pin is forced progressively against the trapped material. During the inward movement of the pin the pin acts as a conical wedge to spread the bore radially and the zone of the expanding pressure lengthens progressively with the progressive longitudinal movement of the pin. If the pin is tapered the lengthening zone of radial expanding pressure may be of substantial axial extent, anda feature of our novel arrangement is that the axial diminsion of the pin taper may be, and preferably is, substantially greater than the initial axial extent of the bore hole taper so that the length of the zone of mutual contact of the two cooperating sealing surfaces increases progressively as the pin moves inward and as. internal pressure of the trapped fluent material rises progressively.

The employment of an oversize pin causes the rivet shank to be expanded radially, and one object of the preferred form of our invention is to provide a pin that will cause the shank to be expanded against the surrounding work material. In this regard the invention is characterized by the concept of employing a pin having a gradual taper extending substantially through its length whereby a wedging force with radial components of tremendous magnitude may be attained.

Fig. 1 shows a rivet body generally designated l0 having a preformed head II and a shank l2. The rivet body ill is provided with a blind axial bore generally designated l3, the bore being divided into an inner portion [5 of substantially uniform diameter and an outer entrance portion l6 that is of tapered or conical configuration. Various materials may be employed to fabricate such a rivet in various practices of the invention, materials such as steel, brass, copp r, aluminum and suitable alloys.

A quantity of suitable fluent material--is .-placed in the rivet bore l3 either at the time the rivet is manufactured for stock or at the time the rivet is I actually used, and the rivet bore maybe filled;

formed. At one extreme a light liquid such as thin oil or water may be employed and at the other extreme a normally solid material, for example, a soft metal alloy, may be employed providing that the normally solid material becomes fluent to an operative extent under the pressure created by a heavy impact tool and/or at the temperature at which the rivet is set. In one practice the rivet may be filled with a normally solid material such as lead or a suitable salt, and in preparation for the rivet-setting operation, the rivet body may be heated to make its content molten and to temporarilymake the rivet body itself more ductile. For most riveting operations, we prefer to employ a non-corrosive liquid or semi-liquid which may be introduced into the rivet bore and then retained by insertion of the pin. Other deformable plastic material, such as white lead, may be used, the material being molded into sings and then rammed into the rivet bore and tamped free of air.

The pin or plunger that is to be driven into the rivet bore hole may be of any suitable material and configuration. The pin should be harder than the rivet body I! but may be of the same material if given additional hardening treatment.

The particular pin 20 shown in Fig. 2 is formed with a chamfer or inclined shoulder 2| at its I outer end and is tapered-throughout its length at the same taper as the entrance portion l6 of the rivet bore.

Fig. 2 shows therivet in initially seated in the tion is that the dimensions of this clearance are not critical, since the shank of the rivet will ex- It will be noted that the rivet body fits pand during the setting operation to conform.

with surrounding rivet holes of various diameters. Fig. 2 shows the-pin 20 in the initial stage of the insertion-of the pin in the rivet body Ill, the I rivet body having 4 been previously filled with suitable fluent material" to approximately the level indicated in 1. .As the pin moves." initially into-the rivet; displacing the fluent material, the annuiarclearance'fl between the rivet and the surrounding rivet bore constitutes a relief passage throughwhich'the fluent material is extruded to accumulate in a mass 28 on the head of the rivet. The annular clearance 21 progressively narrows and the first stage of the 6 sertion of thepin 20 has been carried out, the

pin being driven beyond the sealing point sufliciently to create an effective seal and to prevent subsequent accidental withdrawal of the pin. One advantage of such a practice is that the protruding pin provides a finger grip by means of which the rivet may be conveniently lifted and applied to work material.

In the second stage of insertion of the pin 20, the pin progressively displaces the fluent material with what may be termed a hydraulic eifect inasmuch as the tremendous pressure created by the displacement'is exerted substantially equally in all directions. During this second stage of insertion, terminating when the pin reaches its ultimate position, for example the ultimate position shown in Fig. 4, the following important eifects occur concurrently:

(1) The frictional and fluid-pressure resistance to the inward movement of the pin causes the rivet body, fluid and pin to act when the pin is struck as a single solid element and thus causes ,the preformed head ll of the rivet to be pressed strongly against the outermost member 23;

(2) While the outer or preformed head ll of the rivet is pressed against the outer member 23, the inner end of the rivet is expanded hydraulically to form the inner head (Fig. 4), which inner head engages the inner member 24 and cooperates with the preformed head II to clamp the. two members 23 and 24 together;

(3) The tapered pin 20 progressively expands the shank l2 of the rivet against the surrounding rivet holes 22 in the members 23 and 24;

(4) Over a relatively long axial dimension, the

tapered pin continuously engages the material of the surrounding rivet with a wedging action that (5) The axial dimension of the rivet bore along -which sealing pressure is exerted increases as the pin is driven home;

(6) [The pin becomes unitary with the rivet to serve as a hard core giving the rivet shank greater strength than the shank of a conventional rivet of the same dimension, especially strength to v withstand shearing stress.

inward movement of 'the pin terminates when I the tapered periphery of 'thepin makes intimate contact with the surrounding tapered portion of the rivet bore.. Since the pin and the entrance portion is of the rivet bore have substantially the same taper, the'closing contact of the pin with'the surrounding rivet occurs substantially simultaneously throughout the entire length of the tapered portion of the bore hole. Even if the pin 20 is moved into the rivet in .a very gradual manner by a steadily applied force, the trapping of the fluent material in the blind end of the bore is decisive and is followed immediately by a rapid rise in the sealing pressure exerted between the pin and the surrounding rivet. In the preferred practice of our invention the pin is driven into the rivet by closely successive blows delivered by an impact tool, in which procedure the sealing contact of the pin with the rivet bore is instantaneous and is instantaneously followed by a sharp rise in sealing pressure.

In one practice of the invention the rivet is placed in stock after the initial stage of the in- Whe Jul pin" is driven flush with the" preformed head I l of the rivet, the same impact tool that is employed to drive the rivet may be used to peen the material. of the rivet head over the chamfer or shoulder 2! as shownin'Fig. 4.

It is apparent that by virtue of such peening,

the rivetfbody engages the pin 20 in a positive manner to lock the pin in place and the pin in turn hydraulically locks the inner end of-the rivet .in the expanded configuration represented by the inner headdesignated 29. Instead of, or in addition to, 'peening the material of the rivet body over the end of the pin we may employ the expedient of toughening or serrating a portion of the pin surface to encourage engagement of the pin by the surrounding metal of the rivet, but it is to be noted that in the absence of any such expedient the tremendous pressure with which the rivet body 'embraces'the pin eflectively terial may be readily controlled and predeter mined in designing the rivet combination and likewise the volume of'the fluent material that is trapped at the end of the first stage of insertion may be easily controlled and predetermined. In addition, the extent to which the fluent material is displaced to expand the inner end of the rivet in the final stage of the pin, insertion may be controlled and determined in advance. All these factors may be computed on the drafting board to arrive at a design of the rivet body and pin suitable for a given riveting task.

Various empirical procedures may also be employed to arrive at satisfactory designs. For example, a rivet body of the general configuration shown in Fig. 1 may be dimensioned for a given rivet hole in work material and then the proper dimensions of the pin may be determined experimentally. The experimental pins used in such a design procedure may be relatively long to permit the experimental pins to be shortened at either or both ends as the experiments may indicate. Cutting off the smaller end of the tapered pin correspondingly increases the volume of the fluent material that is trapped when the pin reaches the sealing position at the end of the first stage of the insertion. If the pin is to be driven flush with the preformed head of the rivet as indicated in Fig. 4, cutting off the larger end of the pin decreases the extent to which the pin is driven into the rivet bore and correspondingly decreases the extent to which the trapped fluent material is displaced in the final stage of pin insertion.

Fig. 5 illustrates a second practice of our invention in which a slide-valve action is employed to cut off extrusion of the fluent material'in the course of the rivet-setting procedure. In Fig. 5 a rivet generally designates 36 has a preformed head 3|, a shank 32, and an axial bore 35 which bore may be initially of substantially uniform diameter. A suitable pin 36 of uniform diameter but preferably formed with a tapered nose 31 may be oversize with respect tothe axial bore 35 so that the pin may function as a conical wedge to axial bore 53 to a suitable intermediate point of the bore. When the oversize pin 55 is driven into the axial bore 53 fluent material 51 in the bore escapes along the groove 56 until the groove is cut oif by the leading end of the pin, whereupon the residual fluent material is trapped for hydraulic expansion of the rivet.

It is apparent that in the embodiment shown in Fig. 6, as well as in the embodiment shown in Fig. 5, the extent to which the rivet is expanded enlarge the axial bore and thereby expand the shank 32 into intimate contact with the surrounding work material. A longitudinal recess 33 is cut in a leading portion of the pin 36 to permit fluent material 46 in the rivet bore to be extruded as indicated at ll until the trailing end of the recess is cut off by the axial movement of the pin, whereby the residual volume of the fluent material is trapped. Upon further movement of the pin the trapped fluent material is displaced to expand the hydraulic rivet in the manner previously described.

Fig. 6 shows another embodiment of our invention in which a slide-valve action occurs in the rivet-setting procedure. The rivet generally designated 56 has a preformed head 5|, a shank 52,and an axial bore 53 that may be initially of uniform diameter. To set the rivet, an oversize pin 55 of the same configuration as the previously described pin 36 is driveninto the axial bore 53. In this particular construction provision for escape of excess fluent material is made by forming a relief channel in the rivet body, for example, a

hydraulically by driving the pin flush with the preformed head of the rivet may be varied simply by varying the lengths of the channels provided for initial extrusion of the trapped fluent material.

In one practice of our invention for which the construction shown in Figs. 5 and 6 is admirably adapted the material for hydraulic action is trapped in the rivetat the time of manufacture and the whole rivet is heated to make the trapped material suitably fluent at the time of installation. Such a practice requires thatthe pin effectively retain the mass of material inside the rivet over an extended period of time and requires some provision to permit the entrapped material to expand under heat without dislodging or loosening the rivet pin. In this practice of the invention the required material, for example melted solder, is placed inside the rivet shown in Fig. 5 or the rivet shown in Fig. 6, and then the corresponding pin is forced into'the rivet in the usual manner to trap the material. The inward movement of the rivet is stopped with escape for the material almost but not quite cut off, the

avenue of egress being sufliciently restricted to retain the material and yet being adequate to permit escape of the material as may be required to compensate for expansion when the rivet is heated. Only a slight inward movement of the pin is necessary to completely out off egress of the fluent material when the rivet is finally used.

In this-last practice of our invention we may employ a rivet such as shown in Fig. 'I. The rivet body 66 in Fig. 'I has the usual preformed head 6|, shank'62, and blind axial bore 63, the bore in this construction being ofsubstantially uniform diameter. A pin is dimensioned for a driving ,flt in the bore 63 and is provided with an axial passage 66 of small cross-sectional dimension. The inner end of the rivet 'bore 63 may be fllled with a normally solid material such as solder. When the pin 65 is driven into the rivet the axial passage 66 permits the escape of air from the interior of the rivet and permits the innerend of the pin to make intimate contact with the entrapped material. When the rivet is taken out of stock and heated, the axial passage 66 permits sufllcient egress of the fluent material to compensate for heat expansion of the material. Even if the trapped material is oil, the axial passage 66 through the pin may be dimensioned to effectively retain the material in the rivet and yet serve as a vent to permit expansion of the material without causing axial movement of the pin. When the pin 65 is driven into the rivet to set the rivet, the impact tool striking the outer end of a the pin cuts ofi the ax al passage at each blow tion will readily suggest various substitutions and changes within the scope under our inventive partures that lie within the scope of our appended claims. v

We claim as our invention: 1. In a rivet for insertion through and beyon registered rivet holes of a plurality of members for interconnecting the members, the combination of a rivet body forming a head and a shank, said body having a blind bore extending longitudinally through said head into said shank; a a

' concept, and-we reserve the right to all such defluent material until said pin is inserted to a predetermined point of sealing with said tapered bore portion whereby an excess volume of the fluent material may be placed in the bore and be reduced automatically to a predetermined volume by insertion of the pin. I

2. In a rivet for insertion through and beyond registered rivet holes of a plurality of members for interconnecting the members, the combination of: a rivet body forming a head and a shank, said body having a blind bore extending longitudinally through said head into said shank; a mass of fluent material in said blind bore; and a plunger adapted to be driven into said blind bore against said fluent material to displace the fluent material outwardly, thereby to radially expand the shank of the rivet in the zone beyond "said registered holes into greater diameter than the registered holes, there being a channel formed in said rivet body providing communication between the exterior thereof and a point in saidblind bore to permit escape of said fluent material from the blind bore until said plunger is inserted past said point whereby any excess fluent ma-,

terial is extruded automatically by insertion of the plunger, leaving apredetermined quantity of the fluent material trapped in the blind bore.

3. In a rivet for insertion through and beyond registered rivet holes of aplurality of. members for interconnecting the members, the combination of: a rivet body forming a head and a shank, j

said body having a blind bore extending longitudinally through said head into said shank; a

mass of fluent material in said blind bore; and a plunger adapted to be driven into said blind bore against said fluent material to displace-the fluent material outwardly by hydraulic action, thereby to radially expand the shank of-the rivet in the zone beyond said registered holes into greater diameter than the registered holes, a leading portion of said plunger being recessed to a point intermediate its forward and rear ends to permit escape of said fluent material from the blind bore until said plunger is inserted to anextent sumcient to close the rear end of the recess, whereby an excess volume of the fluent material may be placed in the bore'and then be reduced automatically to a predetermined volume by insertion of the plunger.

4. In a rivet for insertion through and beyond registered rivet holes of a plurality of members for interconnecting the members, the combination of: a rivet body forming a head and a shank, said body having a blind bore extending longil0 tudinallythrough said head into said shank; a mass of fluent material in said blind bore; and a pin adapted to be driven into said blind bore against said fluent material to displace the fluent material outwardly by hydraulic action, thereby to radially expand the shank of the rivet in the zone beyond said registered holes into greater diameter than the registered holes, therebeing a' v passage in one of said rivet. body and pin elements efiective for escape of said fluent material from said bore until said passage is closed byoverlap of the other of said elements when said pin reaches a predetermined point in the blind bore, whereby any excess volume of the fluent material in the blind bore is reduced automatically to a predetermined volume by insertionfof the pin, said pin being of a length toproduce a desired'extent of displacement of said -prede-. termined volume of the fluent material when the pin is driven substantially completely into the rivet body.

v 5. In a rivet for insertion through-and beyond registered rivet holes of a plurality of membersplunger being oversize with respect to the blind bore to move in the blind bore with a wedging action, thereby to create sealing pressure to minimize leakage of the fluent material past the plunger as well as to expand the blind bore and increase the diameter of said shank within said registered holes.

6. In' a rivet for insertion through registered rivet holes of a plurality of members for interconnecting the members, the combination of:--

a rivet body forming a head and a shank, said body having a blind bore extending longitudinally through said head into said shank: a mass of fluent material in said blind bore; and .a plunger adapted to be driven into said blind bore against said fluent material to displace-the fluent material outwardly by hydraulic action, thereby to radially expand the closed endof the shank 'of the rivet into greater circumfereneethan the;

remainder of said shank can attain when conflned bysaid registered holes having such diameter thatsaid shank initially bears a normal flt-' ting relation thereto, at least a portion of said blind bore extending tothe entrance-thereof being tapered and at least a portion of saidplunger extending t0; the leading end thereof being of i the same taper, whereby in the course of inser-- tion of the plunger the plunger initially'forms with the blind bore a passage for escape of the fluent material and then forms with the blind bore an annular seal of substantial axial extent against leakage of fluent material from the blind.

- of the blind bore, whereby the axial extent of said annular seal increases as the plunger continues 1 to move into the blind bore.

8. In a rivet for insertion through and beyond registered rivet holes of a plurality-of members 11 for interconnecting the members, the combination of: a rivet body forming-a body and a shank, said body having a blind bore extending longitudinally through said head into said shank; a mass of material in said blind bore adapted to be heated to fluency at the time the rivet is installed; and a pin partially inserted in said bore, thereby retaining said material while the rivet is in stock prior to installation, there being a relatively small vent passage from the interior of the rivet eflectivewhile the pin is thus partially inserted to permit expansion of said material under heat prior to installationwithout dislodging the pin, saidpartially inserted pin being adapted to be driven further into said bore thereby to cut ofl said vent passage and displace the fluent material to radially expand the shank of the rivet in the zone beyond said registered holes into greater dimension than the registered holes.

9. In a rivet for insertion through registered rivet holes of a plurality of members for interconnecting the members, the-combination of: a rivet body forming a shank of deformabl metal and a head. said body having a blind bore ex-.

tending longitudinally throughsaid head into said shank; a mass or substantially incompressible fluent material in said blind bore; and

12 a plunger adapted to be driven into said blind bore against said fluent material to displace the fluent material by hydraulic action, said plunger being oversize with respect to said blind bore and of harder metal than said body, whereby said shank is reinforced by said plunger against deformation.

JUSTIN ARNOLD VARNEY.

FRED M. VARNEY.

NORMAN J. HOLTER.

REFERENCES CITED The following references are of record in the tile of this patent:

UNITED STATES PATENTS 

